Skin Cancer 
Acute phototoxic reaction
Dermatoheliosis
Carcinogenesis
Ultraviolet light is the most important carcinogen for the genesis of skin cancers.
- ultraviolet C
- highly carcinogenic, with wavelengths < 290 nm
- however, it does not reach the earth surface in significant amounts because of ozone layer
- ultraviolet B
- most carcinogenic band that reaches earth in significant quantity
- band of ultraviolet radiation between 290 and 320 nm
- ubiquitous during daylight hours
- directly damages DNA, causing strand breaks and nucleotide dimer formation
- ultraviolet A
- is light between 320 nm and 400 nm
- a weak carcinogen by itself, but in combination with UVB has significant additive effect
- small amounts are important for vitamin D synthesis
- major carcinogenic effects of large amounts of UVA are in the band between 320 and 340 nm
- biologic damage is direct, similar to the type induced
by UVB
in turn interact with DNA
